The custom ivory dress designed by Costa included 6,000 pearls of various sizes.

Representatives for the actress reported the theft. Detectives suspect the garment was stolen sometime between 8 and 9 p.m. Wednesday, sheriff's Lt. William Nash said.

Detectives were at the hotel Thursday looking for clues, including whether surveillance footage would reveal what happened to the gown.

Nyong'o won an Oscar in 2014 for her role in "Twelve Years a Slave" and was a presenter at Sunday's ceremony.

Her publicists said Thursday they would not comment on the theft.

Nyong'o, 31, has become a darling of Hollywood's red carpets in the past two years, with commenters and fans praising her fashion choices.

She accessorized the dress with Chopard diamond drop earrings and three Chopard diamond rings. Before the awards ceremony, she told The Associated Press on the red carpet, "I'm just wearing my diamonds and pearls. My homage to Prince," referring a popular song by the musician.

Nyong'o told a reporter for Yahoo Style that she was involved in the design process of the dress.

"We talked about it being fluid and liquid," she told the site. "I wanted it to be an homage to the sea."